Surprises in the rock pools

Rock pooling can be an emotional experience and I’ve experienced everything from happiness to horror in the last couple of weeks. The arrival of warmer weather has brought out a joyous burst of extraordinary colours in the pools and plenty of surprises too.

I’ve picked out some of the best below, but I’d suggest you put down your food before you read the last one.

Colours in the rock pools at Porth Mear – painted topshell

It’s never easy to run in knee-deep water and across slippery rocks wearing wellies, but I came close to setting a new land-speed record after hearing the cry of, ‘Octopus!’ from across the shore at Lee Bay.

The timing couldn’t have been better. I was teaching a Coastal Creatures workshop on molluscs in North Devon and here was the mollusc I’d been hoping to find for decades.

Experienced local rock pooler, Rob Durrant of Coastwise North Devon, found the Curled octopus (Eledone cirrhosa) hiding under a rock. With quick thinking, he scooped it into a transparent pot where it demonstrated its great ability to change shape and colour, blanching almost to white when we placed it in a white bucket.

Curled octopus (Eledone cirrhosa). Cephalopod molluscs have complex eyes which evolved completely separately from our own eyes and have a distinctive long pupil. Photo by Rob Durrant.Curled octopus looking paler as we placed it in a white bucket – it also changed its skin texture.

Octopi are natural escape artists. Because they have no bones, they can squeeze into incredibly tight spots. This one seemed to enjoy the safety of its pot and it took some effort to persuade it to swim free in the pool.

Curled octopus (Eledone cirrhosa). This species has a single line of suckers down its arms, which tend to curl at the tips. Photo by Rob Durrant.

One of the volunteers asked me to verify what species of pipefish a participant had found. The fish did have a long snout like a pipefish, but on closer inspection I could see its body was thickened in the middle, and in front of its dorsal fin was a row of flattened spines.

15-spined Stickleback (Spinachia spinachia) in Looe

The fifteen-spined stickleback (Spinachia spinachia) is a species I’ve only seen a couple of times before. It’s elusive and easily overlooked, but it is a remarkable fish. In addition to having the most beautiful, tiny mouth, it also has an fascinating life cycle. The male fish builds a nest, arranging fronds of seaweed just-so before the female lays her eggs in it. The female fish dies soon after laying, leaving her mate to guard the nest of eggs until they hatch.

15-spined stickleback about to be returned to its pool

On the same day, we had another surprise, a corkwing wrasse swam straight into Other Half’s bucket.

Inside the bucket, a fish with bold turquoise stripes across its face was swimming at an awkward angle, looking at me through a wide orange eye. Pretty though it was, it was something just behind its eye that Other Half was pointing at. He needn’t have bothered: I was already staring at it.

I wasn’t sure I wanted to see it, but I couldn’t help looking.

No doubt, like me, you’ve heard of fish lice. They’re generally tiny copepods, a kind of swimming baked bean, that attach to a fish and suck its blood. They’re the sort of thing that can put you off your lunch, but you accept it’s part of nature.

This thing, on the other hand, was straight out of an alien movie.

Corkwing wrasse with parasitic isopods (Anilocra physodes)

Far from tiny, this parasite was at least a quarter of the length of the fish.

It was a giant, woodlouse-like animal, a marine isopod, clamped onto the fish by its jaws. On closer inspection, there were other, smaller isopods of the same sort on the fish.

Enough to put you off your food – Anilocra physodes parasitic isopods feeding on the wrasse.

I’d never seen anything like it – and would be happy not to again. I’ve come across many grim feeding habits on the shore, but never imagined that I’d see a parasite this large.

It was the find of the day, even if it did make me feel a touch nauseous.

Several people at the ramble asked if we should remove the parasite. However horrific it looks to us, all these animals are part of the ecosystem and they have to feed, so it’s best not to interfere.

It turns out that there are a couple of species of isopod that target wrasse. This one is Anilocra physodes, confirmed by David Fenwick of Aphotomarine. David suggests looking out for another isopod that replaces the tongue in weever fish. Yes, you read that right! I have no idea how to go about looking in the mouths of weever fish.

It goes to show that there’s no end of surprises on the shore.

To allow you to get back to your food, here are some less alarming rock pool finds from the recent spring tides.

Wow – must have been a surprise to reel that in! Amazing animals and I’m massively excited to finally have had the chance to see one on the shore. I’m hoping the weather stays good for the rest of the summer now … still so many more things to see out there! 🙂